Optically active salicylaldimine copper complexes are known to be useful as catalysts for a variety of organic synthetic reactions. For example, an optically active salicylaldimine copper complex which is obtained by reacting optically active N-salicylidene-2-amino-1,1-di(2-isopropoxyphenyl)-1-propan-ol with copper acetate (II) is known to be useful as a catalyst for asymmetric cyclopropanation (Japanese Examined Patent Publication JP-B2 S53-43955). In the reaction of the optically active N-salicylidene-2-amino-1,1-di(2-ispropoxyphenyl)-1-propanol with the copper acetate (II), acetic acid is by-produced as the reaction progresses. Since this byproduct acetic acid may inhibit the catalytic reaction or may corrode a reaction apparatus, it is necessary to conduct an operation of removing the by-produced acetic acid by neutralization using bases such as sodium hydrogen carbonate.